The machine causing issues is an iMac desktop PC but with Windows 8 as the only OS, this is the only one we have in the office, all others run Mac OS X with Windows 8 running on VMWare, so cannot replicate the exact set up to test on other machines.

The spreadsheet automatically opens as a read only file on the problem machine, but on others opens as fully editable, is there a setting in excell 2013 that would cause this?